Rotary actuator



Feb. 16, 1965 OWENS E L 3,170,097

ROTARY ACTUATOR Filed Oct. 19, 1961 3'5. 2 INVENTORS W.M. OWENS BYW/LFRED HUNTER HIS flTTOEA/EVS United 1 States Patent 3,179,097 ROTARYACTUATOR William M. Owens and Wilfred Hunter, Hertfordsliire, England,assignors, by mesne assignments, to Ledex, Inc., Dayton, Ohio, acorporation of ()hio Filed Oct. 19, 1961, Ser. No. 146,190 Claims. (Cl.317-192) This invention relates to rotary actuators adapted to convertan axial thrust to rotary movement and more particularly to an improvedrotary actuator construction of the type described and claimed inassociation with an electromagnetic actuator in United States LettersPatent, No. 2, 496,880, issued to George H. Leland, granted Feb. 7,1950; however, the invention is not necessarily so limited.

An object of the present invention is to provide an improved mechanismfor converting axial movement into rotary movement.

The basic mechanism, in its original form shown in the aforesaid patent,No. 2,496,880, constitutes a rotary solenoid comprising a fixed assemblyincluding a housing and an electromagnet and a movable assemblyincluding an armature and an output shaft. The armature is movabletoward the magnet upon energization of the magnet while the output shaftis connected with the armature for rotation when the armature isattracted by the magnet. A plate is secured to the shaft connected withthe armature and arranged in opposed relation to a surface portion ofthe housing. The plate and the aforesaid surface portion are separatedby rotatable elements, preferably balls. The plate or the housingsurface, or both of them, are provided with arcuate, inclined recessespresenting cam surfaces arranged with relation to the balls such thatthe action of the cam surfaces on the balls will cause the plate andarmature to rotate when the armature is attracted toward the magnet.Specifically, the plate is normally biased so that a ball element islocated within the shallow end of its recess, or recesses, as the casemay be. Upon attraction of the armature toward the magnet, the ballelements are forced to roll along their corresponding recesses towardthe deeper ends thereof. After each energization of the coil, the shaftand plate are returned to their initial positions at the shallow ends ofthe recesses.

This particular rotary mechanism has found wide commercial success inits original form and with minor variations. Units commerciallyavailable are typically capable of a million or more repeatedoperations. After extended use, however, portions of the mechanism aresubject to wear and the rotary actuator in time operates eratically. Toconfine the ball elements between the plate and the opposed housingsurface, a flange is secured to the shaft adjacent another surface ofthe fixed assembly. We have found that one of the greatest sources ofbreakdown of actuators of this type is this flange. The flange becomesworn and may even be severed from the shaft since it repeatedly strikesthe adjacent surface of the fixed assembly as the plate and shaft returnto their initial positions.

A further object of this invention is to prolong the useful life ofrotary actuators of the type described above.

Other objects'andadvantages reside in the construction of parts, thecombination thereof, the method of manufacture and the mode ofoperation, as will become more apparent from the following description.

In the drawings:

FIGURE 1 is an end 'elevational view of a rotary solenoid unit embodyingthe improvement of the present invention.

FIGURE 2 is a sectional view taken substantially along the line 2-2 ofFIGURE 1.

FIGURE 3 is an enlarged fragmentary sectional view taken substantiallyalong the line 3-3 of FIGURE 1.

Referring to the drawings in detail, the rotary solenoid comprises ahousing which is preferably cylindrical in form and which includes aferromagnetic cup-shaped casing 10 closed by a back wall or closure 12for the open end of the casing. A ferromagnetic element 14 is arrangedconcentric within the casing 10 and press fit therein. A cylindricalinwardly directed portion of the element 14 provides a core 16 for thesolenoid. The back wall 12 may be secured to the element 14 by screws 15provided with heads (not shown) engaged within wells or recesses in theelements 14. An annular solenoid coil 18 extends about the core 16within the casing 10, the coil being separated from the core and thecasing by a suitable insulating member 20. The coil 18 and core 16comprise a conventional electromagnet which may be electricallyenergized through suitable leads (not shown). The casing 10, theelectromagnet and the back wall 12 remain in a fixed position throughoutnormal operation of the actuator. Hence, these elements are collectivelytermed a fixed assembly herein.

The central portion of the back wall 12 is apertured, the edges of theaperture being bent so as to form a rearwardly projecting annular springhousing 22 which encircles a coil return or reset spring 24, the purposeof which will be described later. An output shaft 26 is journalled forrotation in an aperture extending axially through the center of the core16, concentric with the sides of the cup-shaped casing 10 and the springhousing 22. A cylindrical armature 30 is fixedly mounted upon the frontend of the shaft 26. For this purpose, the armature 30 is provided witha central bore or axial aperture 32 while the forward portion of theshaft 26 is splined or knurled as indicated at 34 and press fit withinthe bore 32. The armature 30 and shaft 26 are permitted to slide axiallyrelative to the fixed assembly. Therefore, the smaller diameter of thecoil 18 is larger than the diameter of the armature 30 so that thearmature 30 may move axially therein. Limitations upon the axialmovement of the armature 30 and the shaft 26 will be discussed below.

It is evident that the magnetic field created upon energization of thecoil 18 will draw the armature 30 axially into the casing 10. This axialmotion is converted to a rotary motion to be impressed upon the armature30 and the shaft 26 by the following means. Integral with the cup-shapedcasing 10 and forming an apertured base or end portion thereof is anannular inwardly directed flange or surface portion 36. The surfaceportion 36 may be termed a fixed plate. The aperture within this platehas a diameter slightly greater than that of the armature 30, so as notto restrict its axial motion; The casing 10, including its flangeportion 36, is ferromagnetic to provide a flux path for the magneticfield created upon energization of the coil 18. For best performance,the air gap between the plate or flange portion 36 and the armature 30is as small as possible.

A movable disc or plate 38 is rigidly attached to the armature 30 foraxial and rotary movement therewith in spaced relation to the outersurface of the flange portion or fixed plate. The opposing surfaces ofthe disc 38 and the flange portion 36 are each provided with threeequally spacedarcuate inclined recesses 40 and 42, respectively. Thedisc or plate 38 is oriented initially with respect to the flangeportion 36 such that the ends of the recesses 40 are substantiallyaligned with the ends of the recesses 42 of the flange portion 36. Asshown in FIGURE 3, the bases of the recesses 40 and 42 are oppositelyinclined. Disposed between each pair of opposing recesses 40 and 42, andin contact therewith, is a rotatable element, shown in FIGURES 2 and 3as a ball bearing 44.

The spring 24, which is attached at one end to the spring housing 22 andat its other end to the shaft 26, biases the shaft 26 and plate 33 intoa position wherein the ball bearings 44 normally occupy the extremeshallow ends of the recesses 49 and 42. To prevent the ballelements-from dropping out of the aligned recesses 4t and 42, a flangeis formed on or secured to the shaft 26 adjacent the rearward surface ofthe ferromagnetic element 14. The flange may conveniently be provided bya snap ring 46 seated within an annular groove in the shaft 2s. The snapring 46 is sufiiciently spaced from the plate 38 to permit the ballelements 44 to occupy the shallow ends of the recesses 40, 42. On theother hand, the plate 38 and the snap ring 46 are sufficiently closethat the plate 3% cannot move away from the flange portion 36 by anamount sufiicient to permit the ball elements 44 to fall out of theopposed recesses 49, 4 2. Therefore, the ball elements 44 always remainconfined between the plates 36 and 53.

In operation, electrical energization of the coil 1% creates a magneticfield drawing the armature 30 into the coil. The plate 38, accordingly,is driven inwardly toward the flange portion 36 of the cup-shaped casingiii. The inclined recesses 40 and 42 cooperate with the ball bearings 44to permit axial motion of the plate 33 only if the plate 3% alsorotates, allowing the ball bearings 44 to roll along the cam surfacesformed at the bases of the recesses 4t 42. That is, relative movement ofthe recesses 4t) and 42 toward the ball elements 4-4 causes the plate 33to rotate. The result is that the axial motion of the armature 3h isconverted to rotary motion of the plate 38. For convenience, the shaft26, armature 3% and plate .38 may be termed a movable assembly. Sincethe movable assembly is driven upon energization of the coil, theresulting operation may be termed a power stroke. FIGURE 3 shows therelative positions of a recess 4%, a recess 42 and a ball element 44 atthe end of a power. stroke. Note that the ball element ts in FEGURE 3 iscupped between the deep ends of the opposed recesses tit and 42.

During the power stroke, the spring 24 is placed under increasedtension. When the coil 18 is deenergized, the spring 24 returns orrestores the movable assembly to its initial angular position, thusresetting the rotary mechanism. This return movement of the movableassembly .may be termed the return stroke. After completion of thereturn stroke, the movable assembly remains biased in its initialposition by the spring 24 until the electromagnet is again energized.

The apparatus described above produes an angular displacement of theshaft 26 each time the coil 18 is energized, the displacement beingcounterclockwise, as viewed in FIGURE 1, for the particular structureshown in the drawings. The direction of rotation during the power strokemay be reversed by inverting the inclina:

tion of the recesses 40 and 42. It is to be noted that, in

this particular embodiment, the shaft 26 is so attached to the armature30 that it is both rotated and driven axially upon each energization ofthe coil 13. Similarly, during the return stroke, the shaft 26 isrotated in the opposite direction by the spring 24. The rotary mechanismconverts the rotary movement imparted to the shaft 26 by the spring 24into an axial movement of the movable assembly outwardly so that thearmature 3:) moves away from thee-ore; 16, that is, to the left asviewed in FIGURE At the end of the return stroke, the ball elements,which are rolling upwardly along the cam surfaces formed at the bases ofthe recesses .40, 42 strike the edges of the extreme shallow ends of therecesses. More precisely, of

course, the extreme shallow end edge of each recess strikes itsassociated ball element while the edge of the extreme shallow end ofeach recess 42, is struck by its associated ball element 44. In priordevices; the snap g 011 the Shaft fil ck the rearward face of theelement 14 at substantially the same time as the ball elements reachedthe shallow ends of the recesses. Thus, the snap ring and the shallowends of the recesses had to absorb much of the momentum of the movableassembly. The impact of the movable assembly against the fixed assemblycaused considerable wear of both the shallow ends of the recesses andthe snap ring. In time, the relatively small snap ring was severed fromthe shaft. When this occurred, the ball elements were no longerconfinedbetween the movable plate and the housing. The actuator thus becameuseless. This problem can be partially remedied by using a large flangeon the shaft. However, the flange must be so massive that it mayinterfere with the normal construction and operation of the actuator.

in accordance with this invention, the useful life of the actuator maybe prolonged without the use of an unduly large flange. Briefly stated,with this invention the impact of the snap ring 46 against the rear faceof the element M is lessened by the provision of means to reducegradually the momentum of the movable assembly at the end of the returnstroke. in the specific embodiment disclosed in the drawing, this meanscomprises yieldable, elastomeric washer 5h that encircles the shaft 26and separates the snap ring 46 from the base of the ferromagneticelement 1e. When the movable assembly completes its return stroke, thesnap ring 46 engages a metal spacer or washer 52 interposed between thesnap ring and the elastomeric 'washer 5t), gradually placing theelastomeric member 59 under compression. Thus, the members 5 3, 52cooperate with the flange 46 to stop the reset movement of the movableassembly. The purpose of the metal washer 52, which is the same size asthe elastomeric member 5i), is to obviate the deterioration of theelastomeric member 5a that would otherwise result should the snap ring46 be permitted to rotatably engage the outer surface thereof. To reducethe axial length of the assembly, the central portion of the rear faceof the ferromagnetic element 14 may be counterbored to provide a pocketfor the elastomeric member 58. The mechanism is so designed that thesnap ring 46 engages the washer 52. at substantially the same instantthe ball elements 44 reach the shallow ends of their recesses.Accordingly, the ball elements 44 remain confined between theseshallowends.

It will be apparent that the interposition of the elastomcric member St}between the snap ring 46 and the base of the ferromagnetic element idserves to provide a shock absorber or damper for the return movement ofthe movable assembly of the rotary actuator, gradually reducing much ofits momentum. The resultant lessening of impact of the snap ring 46 withthe rear face of the element 14 greatly-increases the number ofoperations the actuator may undergo before the snap'ring becomesfatigued and breaks down. As a result, the useful life of rotaryactuators of this type has been extended in some cases by severalmillion operations. Thus, although the change from the known prior artdevices is only of a simple nature, the increase in the useful life ofthe actuator is quite dramatic.

Another advantage gained with this construction is the reduction inimpact of the ball elements M- with the shallow end edges of therecesses 4h, 42. As the elastomeric member 5?; compresses or yields atthe end of the return stroke, the entire movable assembly is permittedto overtravel beyond its normal starting or deenergized position. Theball elements 44 accordingly may cam. slightly outwardly along theshallow end edges of the recesses, or to the left as'viewed in FIGURE 2,while the movable assembly is losing momentum. Thus, the sharp impact ofthe ball elements against the shallow-ends of the recesses is reducedThis serves to prolong the life of theball elements and to reducethewear on the recesses.

Although the presently preferred embodiment of the in the purview ofthis invention various changes may be made in the form, details,proportion and arrangement of parts, the combination thereof and mode ofoperation, which generally stated cons in a device capable of carryingout the objects set forth, as disclosed and defined in the appendedclaims.

Having thus described our invention, we claim:

1. In a rotary actuator: a fixed assembly having spaced first and secondsurface portions and an aperture cornmunicating between said surfaceportions; a shaft journalled for axial and rotary movement within saidaperture and projecting beyond both of said surface portions; a plateconnected to said shaft adjacent said first surface portion, one of saidplate and said first surface portion having an arcuate inclined recesstherein; a rotatable element in said recess interposed between and incontact with said plate and said first surface portion; a flange securedto said shaft adjacent said second surface portion, said flange and saidplate being sufiiciently spaced to pe mit said rotatable elements toengage the shallow ends of said recesses but sufficiently close toconfine the rotatable elements between said plate and said firstsurface; drive means inducing relative axial movement between said plateand said first surface portion whereupon said shaft undergoes bothrotary and axial movement causing said flange to move away from saidsecond surface portion; means to reset said shaft, plate and rotatableelement after each operation of said drive means whereupon said flangemoves toward said second surface portion;

and yieldable means having a greater yielding capacity than that presentin said fixed assembly at the second surface portion thereof interposedbetween said second surface portion and said flange, said flangestriking said yieldable means at the end of the reset movement of saidshaft, said yieldable means and said flange cooperating to stop thereset movement of said shaft.

2. The structure or" claim 1 wherein said drive means includes anelectroinag et forming a portion of said fixed assembly and an armaturesecured to said shaft for movement ther with, said armature beingattracted toward said electromagnet upon each energization thereof.

3. The structure or" claim 1 wherein said yieldable means includes anelastomeric washer encircling said shaft.

4. The structure of claim 3 wherein said yieldable means furtherincludes a metal washer encircling said shaft and interposed betweensaid elastorneric washer and said flange.

5. The structure of claim 3 wherein said second surface is the rearsurface of a core element for the electromagnet, said surface beingcounterbored to provide a pocket for said elastorneric Washer.

References Cited in the tile ofthis patent UNITED STATES PATENTS 2,36,886 Leland Feb. 7, 1950 2,978,915 Metcalf Apr. 11, 1961 2,989,871Straub et al June 27, 1961

1. IN A ROTARY ACTUATOR; A FIXED ASSEMBLY HAVING SPACED FIRST AND SECONDSURFACE PORTIONS AND AN APERTURE COMMUNICATING BETWEEN SAID SURFACEPORTIONS; A SHAFT JOURNALLED FOR AXIAL AND ROTARY MOVEMENT WITHIN SAIDAPERTURE AND PROJECTING BEYOND BOTH OF SAID SURFACE PORTIONS; A PLATECONNECTED TO SAID SHAFT ADJACETN SAID FIRST SURFACE PORTION, ONE OF SAIDPLATE AND SAID FIRST SURFACE PORTION HAVING AN ARCUATE INCLINED RECESSTHEREIN; A ROTATABLE ELEMENT IN SAID RECESS INTERPOSED BETWEEN AND INCONTACT WITH SAID PLATE AND SAAID FIRST SURFACE PORTION; A FLANGESECURED TO SAID SHAFT ADJACENT SAID SECOND SURFACE PORTION, SAID FLANGEAND SAID PLATE BEING SUFFICIENTLY SPACED TO PERMIT SAID ROTATABLEELEMENTS TO ENGAGE THE SHALLOW ENDS OF SAID RECESSES BUT SUFFICINELTYCLOSE TO CONFINE THE ROTATABLE ELEMENTS BETWEEN SAID PLATE AND SAIDFIRST SURFACE; DRIVE MEANS INDUCING RELATIVE AXIAL MOVEMENT BETWEEN SAIDPLATE AND SAID FIRST SURFACE PORTION WHEREUPON SAID SHAFT UNDERGOES BOTHROTARY AND AXIAL MOVEMENT CAUSING SAID FLANGE TO MOVE AWAY FROM SAIDSECOND SURFACE PORTION; MEANS TO RESET SAID SHAFT, PLATE AND ROTATABLEELEMENT AFTER EACH OPERATION OF SAID DRIVE MEANS WHEREUPON SAID FLANGEMOVES TOWARD SAID SECOND SURFACE PORTION; AND YIELDABLE MEANS HAVING AGREATER YIELDING CAPACITY THAN THE PRESENT IN SAID FIXED ASSEMBLY AT THESECOND SURFACE PORTION THEREOF INTERPOSED BETWEEN SAID SECOND SURFACEPORTION AND SAID FLANGE, SAID FLANGE STRIKING SAID YIELDABLE MEANS ATTHE END OF THE RESET MOVEMENT OF SAID SHAFT, SAID YIELDABLE MEANS ANDSAID FLANGE COOPERATING TO STOP THE RESET MOVEMENT OF SAID SHAFT.